Tubular fiber arrangement of a fiber-reinforced composite part

ABSTRACT

In the production of a tubular fiber arrangement as an intermediate product for a composite part, the local conditions are taken into account in an especially simple and reliable manner with respect to the geometry of the composite part and its load profile. When forming the composite part on a core, the fiber mass supplied during the formation of the tube is proportional to the local circumference of the composite part which results from the diameter. The advancement speed of the core remains substantially constant.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of Ser. No. 13/945,069,filed Jul. 18, 2013, which was a continuation, under 35 U.S.C. §120, ofcopending international application No. PCT/EP2012/050650, filed Jan.17, 2012, which designated the United States; this application alsoclaims the priority, under 35 U.S.C. §119, of German patent applicationNo. DE 10 2011 002 840.4, filed Jan. 18, 2011; the prior applicationsare herewith incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a method for producing a tubular fiberarrangement as an intermediate product for a fiber-reinforced compositepart. The tubular fiber arrangement has a cross-sectional shape thatchanges along its length.

Fiber-reinforced composite parts have been gaining increasing popularitybecause, as compared to conventional components, they have acomparatively light inherent weight and they can be produced and used ina particularly flexible manner.

However, conventional fiber-reinforced composite parts are associatedwith a problem in that in the formation of hollow profiles, in which thefibers are arranged on a core, the density of the fiber arrangementfluctuates considerably in accordance with the profile of the core orwith the target shape of the fiber composite part, and consequently weakpoints in the mechanical loadability of what will later be the compositepart can often arise.

For example, in the case of material input that exceeds the necessarymeasure during fiber reinforcement the material costs increase, whilethis also results in geometric problems, namely when as a result ofexcessive material input the geometry of the base body, on which basebody fiber reinforcement is based, is distorted towards the exterior, inother words is not reproduced in the correct proportions.

German published patent application DE 196 25 798 A1 describes a way toavoid producing a textile tube for a motor vehicle driver, which textiletube comprises reinforcement fibers, by tailoring it with considerableexpenditure directly onto a core. There, a textile hose is produced thatcomprises uneven distribution of the fiber material. The distributionhas been preventatively matched to the core shape and which when thehose is pulled onto the core is intended to become uniform. In otherwords an initially denser fiber arrangement later impinges on bulges ofthe core, and thus is intended, after being pulled on, to adapt to thedensity of the fiber arrangement in the remaining region. This isassociated with a disadvantage in that subsequently pulling the tubeonto the core is precisely unlikely to result in this desired effectbecause, for example, when passing over larger core diameters, regionsare widened that are subsequently intended for a smaller core diameter,and in this process fibers or fiber strands are displaced, whichultimately results in uneven strength and stability and thus in weakpoints in the composite part produced.

U.S. Pat. No. 4,228,207 and its counterpart German utility model DE 7826 718 U1 describe the production of a tubular braided fabric with avarying diameter as a flexible formation is known that serves as anintermediate product for rigid but lightweight parts, for exampleresin-impregnated composite parts such as sports articles or forindustrial applications. In order to achieve a desired constantthickness of the braided fabric, in this arrangement the braiding angle,in other words the angle of thread placement relative to thelongitudinal axis of the braided fabric, is varied, i.e. for smallercross sections the braiding angle is reduced by means of an increasedtransport speed during braiding, while for larger cross sections thebraiding angle is increased by means of a decreased transport speed. Inthis manner the direction of the maximum capacity to absorb tensileforces by the fibers, for example glass threads or carbon threads, whichare, for example, used for such components, is changed. Now, assumingthat the direction of thread placement is to correspond as far aspossible to the direction of load of what will become the compositepart, in application of the teaching of this document a more or lesssignificant deviation from the thread placement direction and from thedirection of force introduction occurs, which significantly reduces thesubstance exploitation of the expensive fiber materials and requiresover-dimensioning of the fiber arrangement in order to achieve thenecessary stability values.

In order to adapt a braiding process to the varying cross-sectionalshape of the braided core, we have already proposed (cf. the commonlyassigned German patent application DE 10 201 0 047 193 A1) to flexiblyadapt to the present core diameter the diameter of the so-calledbraiding ring that bundles the braiding threads in front of the braidingpoint. While this does results in a braiding geometry that is moreindependent of the diameter, and thus results in an equalization of thebraiding conditions, it does not, however, solve the problem of thebraiding thickness that varies depending on the diameter.

BRIEF SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide a tubular,hose-shaped fiber arrangement and a corresponding production processwhich overcome the above-mentioned disadvantages of the heretofore-knowndevices and methods of this general type and which provides for afiber-reinforced composite part and a tubular fiber arrangement as anintermediate product for a composite part, wherein the local conditionsare to be taken into account in an especially simple and reliable mannerwith respect to the geometry of the composite part and its load profile.

With the foregoing and other objects in view there is provided, inaccordance with the invention, a method of producing an intermediateproduct for a fiber-reinforced composite part, the method whichcomprises:

forming a tubular fiber arrangement (i.e., a hose-shaped assembly) on acore having a shape corresponding to the composite part, with a varyingcross-sectional shape along a length thereof, the tubular fiberarrangement forming the intermediate product;

supplying fibers during a formation of the tubular fiber arrangementwith a fiber mass being proportional to a local diameter andcircumference of the composite part; and

maintaining an advance speed of the core substantially constant duringthe supplying and forming step.

The method according to the invention ensures to the greatest possibleextent a constant density and thus also thickness of the fiberarrangement, irrespective of cross-sectional fluctuations of the core onwhich the fiber arrangement is formed. In this manner, distortions ofthe geometry of the composite part that will later be formed from theintermediate product of the tubular fiber arrangement are avoided. Aboveall, however, predetermined fiber alignments that are to coincide withwhat will later be the direction of load in the composite part are atleast not noticeably impeded in the case of changes in diameter. Thelatter is also in particular achieved in that, in contrast to the stateof the art, adapting the fiber mass to the particular cross section ofthe core on which the tubular fiber arrangement is formed is notimplemented by differences in the advance speed, which differencesresult in different placement angles.

The fiber arrangement according to the present invention is to beinterpreted as an arrangement of, in particular, coarse-denier threadsor narrow ribbons comprising glass, carbon or other high-strengthmaterials that are commonly used in the production of fiber-reinforcedcomposite parts. Since the diameter or the circumference of the corethat corresponds to the shape of the composite part changes more or lessquickly or strongly, variation of the fiber mass cannot be carried outcompletely synchronously. The term “proportional” in this document thusalso denotes, for example, that progressive adaptation takes place,and/or that the adaptation does not completely cover all the extremitiesof the circumferential values, because otherwise the requirementsconcerning the technical implementation of the variation of the fibermass might exceed the benefit of said implementation.

Advantageously the fiber arrangement is formed from an interlaid scrim.This arrangement uses, in particular, so-called 0°—threads, which extendessentially so as to be parallel to the longitudinal extension of thecore and which are intended to absorb longitudinal forces, and wrapthreads, which extend at angles of between 0° and 90° to thelongitudinal extension of the core. Interlaid scrims are associated withan advantage in that as a result of the avoidance of intersection pointsthat occur in braided fabrics or knitted fabrics, the fibers arearranged so as to be highly stretched, thus providing excellent forceabsorption behavior. An intersecting fiber structure is then, however,well suited to tie the interlaid scrim in order to prevent its mutualdisplacement and in order to fix the thread formation until resinimpregnation takes place at a later stage. Such methods are described,for example, in our commonly assigned U.S. Pat. No. 8,114,793 B2 and itscounterpart international patent application WO 2007/090555 A2, and theyneed therefore not be described in more detail in this document.

In particular a braided fabric can be considered as an intersectingthread structure. However, as an alternative, a knitted fabric structureis suitable to tie the layers of interlaid scrim.

Changing the fiber mass can advantageously be achieved in that thefineness of the supplied threads changes. To this effect by means of aremoval device the number of individual fibers from which the respectivethreads are formed can be reduced, or can be increased by means of anautomated application device. Advantageously, the removal device and theapplication device are combined in one device, because after removal offibers the renewed application of fibers is necessary to achieve theprevious thread fineness. Advantageously, in order to apply fibers,adhesives are used that with regard to subsequent impregnation areresin-based.

Instead of varying the thread fineness of the threads used, adaptationof the fiber mass can also occur, for example by varying the number ofthreads involved in forming the interlaid scrim. Reducing the number ofthreads is achieved by detaching threads. Increasing the number ofthreads is achieved in that, for example, previously detached threadsthat have been kept in reserve are supplied again. In this case, too,fixing the starting ends of the threads can be supported by an adhesive.

In order to determine the local cross section of the composite part orof the core to which the tubular fiber arrangement is to be allocated,mechanical touch sensors or planar photoelectric barrier arrangements orsimilar are imaginable.

With the above and other objects in view there is also provided, inaccordance with the invention, an article of manufacture, whichcomprises:

a tubular fiber arrangement forming an intermediate product for afiber-reinforced composite part having a variable cross-section along alength thereof, wherein said tubular fiber arrangement is formed on acore having a shape corresponding to the composite part;

a fiber mass of said tubular fiber arrangement in a cross section of thecore being proportional to a local circumference resulting from adiameter of the core; and

wherein an alignment of the fibers in the tubular fiber arrangement islargely constant, irrespective of the local circumference of the core.

In other words, the tubular fiber arrangement according to theinvention, which fiber arrangement serves as an intermediate product fora fiber-reinforced composite part, comprises a fiber mass that in thecross section of the core on which it rests is proportional to the localcircumference resulting from the diameter of the core, wherein thealignment of the fibers is largely constant relative to the longitudinaldirection of the core, irrespective of the local circumference of thecore. This results in a uniform structure of the composite part andabove all in reliably good alignment of the fibers in what will later bethe direction of load.

Other features which are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a method for producing a tubular fiber arrangement of afiber-reinforced composite part and tubular fiber arrangement, it isnevertheless not intended to be limited to the details shown, sincevarious modifications and structural changes may be made therein withoutdeparting from the spirit of the invention and within the scope andrange of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 shows two composite parts, each designed in the manner of atruncated cone, the first according to prior art and the secondaccording to the invention;

FIGS. 2 to 10 are diagrams illustrating the method-related procedure inreducing the fiber mass and subsequently restoring the old fiber mass;

FIG. 11 shows a composite part comprising three different diameters andallocation with a thread number that varies according to the diameter;and

FIG. 12 is a schematic of a composite part with a structure comparableto the one illustrated in FIG. 11 for allocation with wrap fibers.

DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawing in detail and first,particularly, to FIG. 1 thereof, there is shown a composite partaccording to the prior art on the left-hand side with a shape of atruncated cone. The prior art device shows the allocation with so-calledstationary threads (0°—threads) 2 with a constant fiber mass along thelength of the composite part 1. This results in a gradually reducedfiber allocation of the circumference of the composite part in thedirection from the small diameter to the large diameter. In the regionof the large diameter the threads are clearly spaced apart, which has anegative effect on the force absorption in the longitudinal direction inthe composite part. In contrast to this, a fiber allocation that overallis more dense would result in the threads overlapping in the region ofthe small diameter, in that said threads are over-dimensioned for forceintroduction, thus resulting in distortion of the geometry towards theexterior. As compared with the above, the embodiment shown on theright-hand side in FIG. 1 of the same fiber composite part shows that inall three sections 3 a to 3 c the average thread spacing is identical.The stationary threads 4 a to 4 c comprise different fiber masses; inother words the fiber mass of the threads 4 a to 4 c decreasesincrementally from the large diameter/circumference to the smalldiameter/circumference. Changing the fiber mass within each section 3 ato 3 c can be ignored. In the sense of the invention the fiber mass issplit proportionally to the diameter or to the circumference of thecomposite body.

Referring to FIGS. 2 to 10, there is shown how the fineness of a threadcan be varied by way of a removal and application device 5. For example,a carbon thread 6 is transported by means of a transport device 7 and issubsequently fed as a stationary thread to a braiding device (notshown). In the braiding device a multitude of stationary threadssupplied in parallel are then tied by intersecting threads.

In the initial position in FIG. 2 the carbon thread 6 has a constantwidth or thread fineness. FIG. 3 shows that by means of a so-calledlabeling device 8 a, 8 b a label is applied for stabilization, whichlabel then reinforces an interface at which the thread width suddenlychanges. In FIG. 4 the section comprising a label is fed to a separatingdevice 9 a, 9 b with a clamping device 10 a, 10 b. FIG. 5 shows that theseparating device 9 a, 9 b is operated while by means of the clampingdevice 10 a, 10 b the carbon thread 6 is affixed in the region ofseparation.

FIG. 6 shows that split-off longitudinal sections 6 b, 6 c of the carbonthread 6 are separated and led away from the clamping device 10 a or 10b.

FIG. 7 shows the further progress of the movement of the carbon thread6, wherein the separated sections 6 b and 6 c and the remaining middlesection 6 a are now longer. Meanwhile the labeling device 8 a, 8 b isactive again and applies a new label at the position at which thesubsequent change in fiber mass is to take place. This is shown in FIG.8, in which in the region of the second label the device 9 a and 9 b andthe clamping devices 10 a and 10 b are active.

FIG. 9 shows the manner in which the separated thread sections 6 b and 6c are removed. Behind the section 6 a with a reduced fiber mass the“normal” carbon thread 6 joins. A carbon thread 6, 6 a treated in thismanner and supplied as a stationary thread would, for example, be usedif a section with a smaller diameter extends between two sections with alarge diameter. This exemplary embodiment is associated with anadvantage in that the removal device and the application device arecombined in one device. This device is suitable for applications inwhich the carbon threads 6 predominantly comprise sections in whichmaximum fineness of the thread is required. Otherwise, fiber removalwould be excessive, although the fibers removed from the carbon thread 6can be recycled. As an alternative it is imaginable to re-use thedetached thread sections in the same process in which they are placedonto the carbon thread 6 at positions where due to a large diameter itis necessary to provide great fineness of the carbon thread.

It is also possible to implement the process of generating sections ofdifferent thread fineness in a discontinuous manner, in other words inincrements. This can, for example, be achieved in that initially threadsare produced that in each case comprise sections with different threadfineness, which threads are subsequently wound onto a carrier. In adownstream process the threads are then pulled off. However, thisrequires very precise attunement of the processes in order to preventthe summation of phase shifts. Such an application may be considered inparticular if identical cores are occupied in sequence, or if compositeparts are produced and in each case at the beginning of a new partsynchronization takes place, for example by removing a thread section orby varying the mutual spacing.

However, it is also imaginable to interconnect different threadsections, in other words thread sections of different fineness. For thispurpose it would be possible, for example, to use a method and a deviceas described in our commonly assigned international patent applicationpublication WO 2008/135 280 A1.

In the version of a composite part 11 as shown in FIG. 11, whichcomposite part 11 comprises the sections 11 a to 11 c the respectivelysupplied fiber mass is varied by the number of the threads 12 that arealso formed as stationary threads. As is shown in FIG. 11, in the regionof the diameter D1, which at the same time is the largest diameter onthe composite part 11, the number of stationary threads are greatest.This section 11 a is followed by a section 11 b, in which the lowestnumber of stationary threads are used, while in the adjoining region 11c, because of the average diameter D3, an average number of threads 12are used. It makes sense, in those positions in which the number ofthreads changes to ensure, by means of an adhesive, that the propersupply of stationary threads can take place. These positions do notrepresent a weak point in later use, because initially this is anintermediate product that receives its final stability byresinification.

FIG. 12 shows that a composite part 13 which as shown by an arrow ismoved, for example, from left to right, is occupied with wrap threads 15a to 15 c that are supplied by means of winding heads 14 a to 14 c. Thesections 13 a to 13 c again comprise different diameters D1 to D3 towhich in each case the thickness of the composite threads 15 a to 15 cis matched so that essentially identical occupation with wrap fibers cantake place irrespective of the particular diameter. For this purpose thewinding heads 14 a to 14 c rotate helically around the composite body 13that is in the process of advancing. The movement of the composite bodyduring the winding process is constant, and consequently the pitch ofthe threads is also constant and corresponds to the placement angledesired with regard to subsequent force introduction. Furthermore, thevarying thread thickness results in the occupation density varying onlyinsignificantly, for example in the transition regions.

In order to ensure that thread placement in the composite componenttakes account of different load directions, as a rule various types ofinterlaid scrim, in other words the application of threads in differentdirections, are/is combined. For example, the process of enteringstationary threads and the process of wrapping could take place oneafter the other on the same basic component, wherein at the beginning ofthe loading process only a core material is present which essentiallyalready has the shape of what will later be the composite part.

Fixing the threads of the interlaid scrim subsequently takes place, forexample by way of a circular braider, as described, for example, in theabove-mentioned U.S. Pat. No. 4,228,207 (corresp. to German utilitymodel DE 78 26 718 U1) or in the above-mentioned German published patentapplication DE 10 2010 047 193 A1. The latter, for example, DE 10 2010047 193 A1 shows the manner in which the transport of the core and theacquisition of the local diameter by way of sensor technology takeplace.

The invention claimed is:
 1. An article of manufacture, comprising: atubular fiber arrangement forming an intermediate product for afiber-reinforced composite part having a variable cross-section along alength thereof, wherein said tubular fiber arrangement is formed on acore having a shape corresponding to the composite part; a fiber mass ofsaid tubular fiber arrangement in a cross section of the core beingproportional to a local circumference resulting from a diameter of thecore; and wherein an alignment of the fibers in the tubular fiberarrangement is largely constant, irrespective of the local circumferenceof the core.
 2. The article of manufacture, according to claim 1,wherein said fiber arrangement has a constant thickness.
 3. The articleof manufacture, according to claim 1, wherein a number of threadsincreases with the diameter of the core to increase the fiber mass. 4.The article of manufacture, according to claim 1, wherein a fineness ofthreads of said fiber arrangement increases with the diameter of thecore to increase the fiber mass.
 5. The article of manufacture,according to claim 4, wherein an average spacing between said threads inrespective longitudinal sections along a length of said fiberarrangement is identical.